1. Field of the Invention
This invention relates to a method of recording information on an optical disc by using a laser beam. This invention also relates to an apparatus for recording information on an optical disc by using a laser beam.
2. Description of the Related Art
It is known to record information on an optical disc in a mark edge recording technique (a mark length recording technique). An example of the recording of information on an optical disc uses a laser beam. Specifically, during the recording of information, a laser beam is intermittently applied to the optical disc while being moved relative thereto. Recording marks are formed in places on the optical disc which are exposed to the laser beam.
In general, the laser beam is generated by a laser diode. To implement the intermittent generation of the laser beam, the laser diode is driven by a pulse signal. In a conventional method, every recording mark on the optical disc corresponds to one drive pulse fed to the laser diode. Furthermore, the length of the recording mark corresponds to the width of the drive pulse. In this case, the heat accumulation effect causes positional and shape errors of the edges of the recording mark.
In a known improved method, every recording mark on an optical disc is caused by a multi-pulse train fed to a laser diode. The multi-pulse train means a sequence of short drive pulses. The duty cycle of the multi-pulse train is chosen to provide a suitable effective recording power of the laser beam at which the heat accumulation effect is sufficiently suppressed. Generally, the width of a first drive pulse in the multi-pulse train is greater than those of other drive pulses therein.
Japanese patent application publication number 11-312311 discloses a method of recording information on an optical disc. In the method of Japanese application 11-312311, a mark data length xe2x80x9cnTxe2x80x9d is determined on the basis of the period xe2x80x9cTxe2x80x9d of a recording channel clock signal, where xe2x80x9cnxe2x80x9d denotes an integer selected from predetermined natural numbers. For the mark data length xe2x80x9cnTxe2x80x9d, a multi-pulse train is fed to a laser diode to form a recording mark on the optical disc. The multi-pulse train means a sequence of short drive pulses. One of drive pulses in the multi-pulse train is remarkably longer than the other drive pulses. Specifically, the long drive pulse has a width equal to or greater than xe2x80x9c1.5Txe2x80x9d while the other drive pulses are equal to or shorter than about xe2x80x9cTxe2x80x9d. In the method of Japanese application 11-312311, a photodiode detects the intensity of a reflected laser beam which results from the reflection of a forward laser beam by the optical disc. During the application of the long drive pulse to the laser diode, the laser beam intensity detected by the photodiode rises and then drops before stabilizing. The detected laser beam is sampled at a moment within the stabilizing stage during the application of the long drive pulse. The sample of the detected laser beam indicates a mark forming condition. Samples of the detected laser beam are generated for multi-pulse trains, respectively. A drive signal to the laser diode which contains multi-pulse trains is controlled in response to samples of the detected laser beam to maintain the mark recording condition in an appropriate range.
It is a first object of this invention to provide an improved method of recording information on a recording medium such as an optical disc.
It is a second object of this invention to provide an improved apparatus for recording information on a recording medium such as an optical disc.
A first aspect of this invention provides a method of recording information on an optical disc. The method comprises the steps of applying multi-pulse trains of a forward laser beam to the optical disc to record mark areas thereon, the multi-pulse trains corresponding to the mark areas respectively; detecting an intensity of a reflected laser beam which results from reflection of the forward laser beam by the optical disc; dividing the detected intensity by a setting intensity to get a division result; detecting a condition of recording of each of the mark areas in response to the division result; and controlling an amplitude of each of the multi-pulse trains in response to the detected condition.
A second aspect of this invention provides a method of recording information on an optical disc. The method comprises the steps of applying multi-pulse trains of a forward laser beam to the optical disc to record mark areas thereon, the multi-pulse trains corresponding to the mark areas respectively; detecting an intensity of a reflected laser beam which results from reflection of the forward laser beam by the optical disc; detecting a maximal intensity of the reflected laser beam which is caused by first one among pulses in each of the multi-pulse trains; dividing the detected intensity by the detected maximal intensity to get a division result; detecting a condition of recording of each of the mark areas in response to the division result; and controlling an amplitude of each of the multi-pulse trains in response to the detected condition.
A third aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of the multi-pulse trains.
A fourth aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises a difference between a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of the multi-pulse trains and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains.
A fifth aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises a ratio between a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of the multi-pulse trains and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains.
A sixth aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises one of (1) a difference and (2) a ratio between a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of the multi-pulse trains and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains.
A seventh aspect of this invention is based on the first aspect thereof, and provides a method further comprising the step of controlling a duty cycle of each of the multi-pulse trains in response to the detected condition in cases where the amplitude thereof reaches its upper limit.
An eighth aspect of this invention is based on the third aspect thereof, and provides a method wherein the detected mean intensity consists of a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of selected ones among the multi-pulse trains, and the selected multi-pulse trains correspond to mark data lengths between 7T and 14T, where xe2x80x9cTxe2x80x9d denotes a channel period.
A ninth aspect of this invention is based on the third aspect thereof, and provides a method wherein the detected mean intensity consists of a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of selected ones among the multi-pulse trains, and the selected multi-pulse trains correspond to a maximum mark data length.
A tenth aspect of this invention is based on the third aspect thereof, and provides a method wherein the detected mean intensity consists of a detected mean intensity of the reflected laser beam which corresponds to a post-head time portion of each of selected ones among the multi-pulse trains, and the selected multi-pulse trains correspond to a mark data length of nT being a later run length, where xe2x80x9cTxe2x80x9d denotes a channel period and xe2x80x9cnxe2x80x9d denotes a predetermined natural number.
An eleventh aspect of this invention is based on the third aspect thereof, and provides a method wherein the detected mean intensity comprises a detected mean intensity based on at least two detected mean intensities corresponding to two of the multi-pulse trains.
A twelfth aspect of this invention is based on the third aspect thereof, and provides a method wherein the detected mean intensity comprises a detected mean intensity based on at least two detected mean intensities corresponding to a common angular position on the optical disc.
A thirteenth aspect of this invention is based on the third aspect thereof, and provides a method further comprising the step of using a filter to get the detected mean intensity, the filter attenuating a signal component having a frequency equal to a frequency of the multi-pulse trains by at least 30 dB.
A fourteenth aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises a detected mean intensity of the reflected laser beam which corresponds to a time point in a later half time portion of each of the multi-pulse trains.
A fifteenth aspect of this invention is based on the first aspect thereof, and provides a method wherein the detected intensity comprises a detected mean intensity of the reflected laser beam which corresponds to pulses except a first pulse in each of the multi-pulse trains.
A sixteenth aspect of this invention provides an apparatus for recording information on an optical disc. The apparatus comprises first means for applying multi-pulse trains of a forward laser beam to the optical disc to record mark areas thereon, the multi-pulse trains corresponding to the mark areas respectively; a photosensitive element receiving a reflected laser beam which results from reflection of the forward laser beam by the optical disc, the photosensitive element generating a current depending on an intensity of the reflected laser beam; second means for converting the current generated by the photosensitive element into a voltage; a low pass filter receiving the voltage generated by the second means for attenuating a component of the voltage which has a frequency equal to a frequency of the multi-pulse trains; a sample-and-hold circuit for detecting, on the basis of an output signal from the low pass filter, a mean intensity of the reflected laser beam which corresponds to each of the multi-pulse trains; third means for dividing one of (1) the detected mean intensity, (2) a difference between the detected mean intensity and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains, and (3) a ratio between the detected mean intensity and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains by a setting intensity to generate a division result; and fourth means for detecting a condition of recording of each of the mark areas in response to the division result generated by the third means.
A seventeenth aspect of this invention provides an apparatus for recording information on an optical disc. The apparatus comprises first means for applying multi-pulse trains of a forward laser beam to the optical disc to record mark areas thereon, the multi-pulse trains corresponding to the mark areas respectively; a photosensitive element receiving a reflected laser beam which results from reflection of the forward laser beam by the optical disc, the photosensitive element generating a current depending on an intensity of the reflected laser beam; second means for converting the current generated by the photosensitive element into a voltage; third means for detecting, on the basis of the voltage generated by the second means, a maximal intensity of the reflected laser beam which is caused by first one among pulses in each of the multi-pulse trains; a low pass filter receiving the voltage generated by the second means for attenuating a component of the voltage which has a frequency equal to a frequency of the multi-pulse trains; a sample-and-hold circuit for detecting, on the basis of an output signal from the low pass filter, a mean intensity of the reflected laser beam which corresponds to each of the multi-pulse trains; fourth means for dividing one of (1) the detected mean intensity, (2) a difference between the detected mean intensity and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains, and (3) a ratio between the detected mean intensity and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains by the maximal intensity detected by the third means to generate a division result; and fifth means for detecting a condition of recording of each of the mark areas in response to the division result generated by the fourth means.
An eighteenth aspect of this invention provides an apparatus for recording information on an optical disc. The apparatus comprises first means for applying multi-pulse trains of a forward laser beam to the optical disc to record mark areas thereon, the multi-pulse trains corresponding to the mark areas respectively; a photosensitive element receiving a reflected laser beam which results from reflection of the forward laser beam by the optical disc, the photosensitive element generating a current depending on an intensity of the reflected laser beam; second means for converting the current generated by the photosensitive element into a voltage; a first sample-and-hold circuit for detecting, on the basis of the voltage generated by the second means, an intensity of the reflected laser beam which corresponds to each of the multi-pulse trains; a low pass filter receiving the voltage generated by the second means for attenuating a component of the voltage which has a frequency equal to a frequency of the multi-pulse trains; a second sample-and-hold circuit for detecting, on the basis of an output signal from the low pass filter, a mean intensity of the reflected laser beam which corresponds to each of the multi-pulse trains; third means for dividing one of (1) the detected mean intensity, (2) a difference between the detected mean intensity and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains, and (3) a ratio between the detected mean intensity and a detected intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains by the intensity detected by the first sample-and-hold circuit to generate a division result; and fourth means for detecting a condition of recording of each of the mark areas in response to the division result generated by the third means.
A nineteenth aspect of this invention provides an apparatus for recording information on an optical disc. The apparatus comprises first means for applying multi-pulse trains of a forward laser beam to the optical disc; second means for detecting an intensity of a reflected laser beam which results from reflection of the forward laser beam by the optical disc; third means for generating a mean of the intensity detected by the second means, the mean corresponding to each of the multi-pulse trains; and fourth means for controlling an amplitude of each of the multi-pulse trains in response to the mean generated by the third means.
A twentieth aspect of this invention provides an apparatus for recording information on an optical disc. The apparatus comprises first means for applying multi-pulse trains of a forward laser beam to the optical disc; second means for detecting an intensity of a reflected laser beam which results from reflection of the forward laser beam by the optical disc; third means for generating a mean of the intensity detected by the second means, the mean corresponding to each of the multi-pulse trains; fourth means for sampling the intensity detected by the second means to generate a first intensity sample corresponding to a maximal intensity of the reflected laser beam which is caused by first one among pulses in each of the multi-pulse trains; fifth means for sampling the intensity detected by the second means to generate a second intensity sample representing an intensity of the reflected laser beam which corresponds to each of intervals between the multi-pulse trains; and sixth means for controlling an amplitude of each of the multi-pulse trains in response to the mean generated by the third means, the first intensity sample generated by the fourth means, and the second intensity sample generated by the fifth means.